EP1087063B1 - Device for drilling and anchoring and method for installing ground anchors - Google Patents

Abstract

The anchor for a building guy cable has a drill tube (8) and a drill tip (12) at one end of the tube. Multiple tension cables (4) are attached to the drill. The rill head is placed in a sealing case (7) formed by injection of cement into the soil surrounding the anchor hole. The anchor tube is removed to leave the dill head and cables embedded in the cement.

Description

The present invention relates to an anchoring device and a method of setting anchor rods intended to ensure the stability of a structure with respect to a terrain, comprising drilling a hole into an anchoring zone in the field, the introduction of cables and / or other tensile reinforcement in the borehole, and the injection by said borehole of a suspension of cement so as to form a seal body in said area anchor.

The usual methods of this type require, for the formation of the sealing body, several cement injections, for example by means of cuff injections, these injections having to be spaced out in time and thus generally requiring several days for the formation of the body. sealing. On the other hand, the force of use remains limited, especially in clay or loamy soils, in particular because of the small cross-sectional dimensions of the sealing body that can be achieved by known methods, the poor control of the formation of this body of its composition. which remains essentially constituted by the injected cement.

The document EP-A-0413676 discloses a method of the above-mentioned type in which a tool is used which has a drilling tool part and has an axial channel extending an injection channel, a valve being disposed at the inlet of said axial channel so as to allow closing said inlet before the injection of a suspension of cement under pressure by the central channel and said axial channel.

The document EP 0 770 734 describes a method in which drilling is carried out by means of a tube provided at its front end with a drilling tool and injection, said tube forming a cement injection channel and said tool having at least two lateral nozzles oriented in opposite directions, and having a drill bit portion having an axial channel extending said injection channel, a valve being disposed between the inlet of said axial channel and said nozzles, so as to allow said inlet to be closed prior to the injection of the cement suspension under pressure, that said cement suspension is injected into the surrounding ground through said nozzles, radially to said tube, with a pressure greater than about 40 MPa (400 bar), by rotating the tube about its axis and back, continuously or discontinuously, over a specified length of seal, which is then stops the injection and that the tube is raised entirely, said cables and / or other tensile armatures being introduced into the borehole, before the hardening of the cement, into the sealing body in formation.

This process makes it possible to considerably shorten the time required for setting up the tie rods and to achieve a good anchorage.

Requirement WO 98/58132 as well as the patent US Patent 3,973,409 each describe a method and an anchoring device in which the tie rod consists of a rigid bar, the liquid cement for forming the seal being introduced into the interior of the drill pipe, directly around said tie rod.

The aim of the invention is to provide an anchoring device and a method for placing improved anchor rods, in particular a device and a method, respectively, of the aforementioned type where the anchoring is further improved and the setting operation in place of anchor anchors simplified and faster.

For this purpose, the method according to the invention comprises the operation of drilling using a drill string. as in claim 1. attached to one or more tie-rods or other tie-bars, that said cement slurry is injected into the surrounding terrain and around the tie-bars and the drill bit, and that the tube entirely leaving the drill bit in the sealing body.

The drilling and anchoring device comprises a column comprising a drill pipe, a drilling tool mounted at the end of the pipe and one or more cables and / or other tie rods, as in claim 3.

The injection tool is preferably provided with at least two lateral nozzles oriented in opposite directions and at least one end nozzle oriented obliquely towards the central axis of the tube in which the cables extend and / or other tensile frames. The drilling tool has a coupling portion which is inserted into the axial channel of the tube axially separable.

During the drilling operation, pressurized water is fed through an axial channel to the drill bit. The axial channel may be formed by an inner tube coaxial with the drill pipe. The inner tube may be provided with a valve, for example in its upper part, to control the supply of water under pressure to the drill bit during the drilling operation and during the operation of the ascent of the drilling column after formation of the sealing body.

The space between the drill pipe and the inner pipe can form the cement injection channel.

The end nozzle is inclined at an acute angle with respect to the axial direction, for example at 30 °, so that the cement suspension jet exiting this nozzle applies a force component in the axial direction on the nozzle. drilling tool. This allows separation of the drill bit from the drill pipe during formation of the seal body. On the other hand, this nozzle ensures that the cables and / or other tie rods are completely embedded in the sealing body.

The device and the method according to the invention thus make it possible to achieve a very good anchoring with very few operations and a great speed.

The invention also avoids problems that may be related to the reintroduction of draft reinforcement in the borehole of conventional methods.

In addition, the attachment of the tensile reinforcement to the drill bit and the pre-insertion into the drill pipe, that is to say before the drilling operation, make it possible to optimize the density of the drill. reinforcement placed in the axial channel of the tube.

The attachment of the drill bit to the end of the tie frames also improves the retention of these reinforcements in the seal body.

• La Fig. 1 est une vue en coupe schématique d'un tirant d'ancrage placé dans un terrain;
• la Fig. 2 est une vue, en coupe axiale, d'une extrémité frontale d'un dispositif de forage et d'ancrage;
• la Fig. 3 est une vue, en coupe axiale, d'une partie de fusible mécanique, à proximité de la tête d'injection, d'un dispositif de forage de l'invention;
• la Fig. 4 est une vue en coupe selon la ligne IV-IV de la Fig. 3; et
• la Fig. 5 est une vue simplifiée, en coupe axiale, d'un dispositif de forage selon l'invention.

The characteristics, aims and advantages of the method according to the invention will emerge more clearly from the description given below by way of example, illustrated in the appended drawings in which:

• The Fig. 1 is a schematic sectional view of a ground anchor placed in a lot;
• the Fig. 2 is a view, in axial section, of a front end of a drilling and anchoring device;
• the Fig. 3 is a view, in axial section, of a mechanical fuse portion, near the injection head, of a drilling device of the invention;
• the Fig. 4 is a sectional view along line IV-IV of the Fig. 3 ; and
• the Fig. 5 is a simplified view, in axial section, of a drilling device according to the invention.

According to the schematic representation of Fig. 1 , a work to be anchored 1 is supported on a part of ground 2 and is stabilized by a tie rod, designated as a whole by the reference 3.

This tie rod comprises, in known manner, for example pulling cables 4 constituted by strands, one end of which is fixed in a pulling head 5 resting on the work 1.

The pulling cables 4 are arranged in a borehole 6 over a certain free length and are secured to a sealing body 7 in the form of a bulb formed around the lower part of the borehole by cement injection under high pressure in the surrounding terrain. The Fig. 1 only gives a schematic representation of an example of a tie rod, the anchoring technique being well known in itself.

The present invention consists in using, for example, a drill string comprising a drill pipe 8 provided with an injection tool 9 coupled to a drill bit 12 according to the invention. Fig. 2 for drilling, first, the hole 6 over a length corresponding to the desired free length and the length of sealing which is basically that of bulb 7 of the Fig. 1 . The drilling tool 12 is attached to the ends of the pulling cables 4, for example by welds 17 or by mechanical clamping means such as keys. The drilling tool 12 and the pulling cables 4 are threaded into the central channel 10 of an inner tube 21 coaxial with the drill pipe 8, before the drilling operation. The drill pipe 8 has a length, without separations, at least equivalent to the length of the tie rods. The drilling tool 12 is coupled to the injection tool 9, axially separable, by complementary teeth 18, or other known mechanical means allowing the rotary drive of the drill bit 12 by the injection tool 9. The drilling tool 12 preferably comprises a tube portion 19 which is inserted into the central channel 10 to allow its radial positioning and retention with respect to the injection tool 9.

The drilling operation is accompanied by an injection of water or a mixture of water and air through the central channel 10 and its extension 11 in the injection tool. The water is injected into the borehole by one or more channels extending axially through the drill bit.

When the drilling is completed, a suspension of cement is injected into the ground at a very high pressure, for example 450 bar, through one or more inclined end nozzles 16 and two or more lateral nozzles 13, 14 of small diameter, ie 1.5 to 2 mm, communicating with one or more axial channels 15 in the injection tool 9. The injection channels 15 are connected to an injection channel 15 'formed between the wall of the tube 8 and the wall of the inner tube 21. A valve (not shown) is arranged in the upper part of the drill pipe to close the central channel 10 during the injection of cement. During this operation, the tube is rotated about its axis and is slowly withdrawn, so that the jets produced by the nozzles 13 and 14 in opposite radial directions penetrate the ground creating a substantially cylindrical bulb, as shown in FIG. Fig. 1 .

The injection pressure is preferably between 500-800 bar. During the injection, it is possible that the injection nozzles 13, 14, 16 clog up with impurities or coarse elements in the cement causing overpressures in the injection channel 15 '. The cement injection pump can be equipped with a solenoid valve to trigger the pump during overpressure. However, during a very sudden increase in pressure, it is possible that the solenoid valve does not have time to trigger sufficiently early to avoid crushing the inner tube. To overcome this problem, the drill string is provided with a mechanical fuse portion 22 comprising a portion of the drill pipe 8 'and an inner tube portion 21' forming between them an injection channel 15 '. The mechanical fuse portion 22 is disposed near the injection head 23, so that in case of deformation, the fuse can be easily exchanged without leaving the drill string of the hole before the end of the operation. cement injection. The inner tube portion 21 'of the fuse portion 22 has a smaller wall thickness than the inner tube 21 of the drill string or other weakening, so that the inner tube portion 21' crushes more easily. the inner tube 21. The crushing of the portion of the inner tube 21 causes the pressure to escape into the central channel 10, avoiding damage to the main inner tube 21.

When raising the drill pipe 8, including the inner pipe 21, the drill bit 12 and the tie rods remain in place and become integral with the bulb 7 during the hardening thereof.

For this purpose, the inclined end nozzle 16 projects a jet against the drill bit 12 so that the tool is pushed towards the bottom of the borehole for that we go back the injection tool 9, thus separating the drill tool from the injection tool. The end nozzle being inclined towards the central channel 10, it also ensures a very good filling of the borehole by the injected cement, so that the pulling cables are completely embedded in the sealing body. In addition, the drilling tool attached to the ends of the tie rods improves their anchorage.

When the sealing body has been formed to the desired length, the injection tool is extracted from the borehole.

As mentioned above, the present invention makes it possible in any case of application to shorten and simplify the anchoring anchor installation procedure, while providing a reliable anchorage, well controlled and high strength in all types of terrain.

Claims (9)

1. Process for forming grout anchors according to which is done the steps of drilling a hole by means of a drilling pipe (8) equipped at its front end with an injection tool (9) and a drilling tool (12) coupled to the injection tool, said pipe having a cement injection channel (15, 15') and said injection tool comprising at least one or several nozzles (13, 14, 16) allowing a cement slurry to be injected under pressure into the surrounding ground in order to form a grout body (7), wherein the drilling tool is attached to one or several anchor cables (4) or other anchoring reinforcements; said cement slurry being injected into the surrounding ground and around the anchoring reinforcements and the drilling tool; withdrawing completely the pipe while leaving the drilling tool in the grout body characterized in that bringing said cement slurry to the the injection tool is done through said injection channel, formed between an inner wall of the drilling pipe and an outer wall of an inner pipe (21) coaxial with said drilling pipe.
2. Process for the placement of grout anchors according to claim 1, characterized in that the drilling pipe (8, 8') is rotated around its central axis while it is withdrawn.
3. Drilling and anchoring device comprising a drilling pipe (8) equipped at its front end with a drilling tool (12) attached to one or several anchor cables (4) or other anchoring reinforcements; such that the drilling tool remains in a grout body (7) formed by cement injection in the ground surrounding a drilling hole (6), characterized in that it further comprises an inner pipe (21, 21') coaxial with the drilling pipe forming between them a cement injection channel, the inner pipe forming a central channel (10) within which the cable and/or other anchoring reinforcements extend.
4. Drilling and anchoring device according to claim 3, characterized in that the device comprises a mechanical safety release part (22) equipped with a portion of drilling pipe (8') and portion of inner pipe (21') coaxial with the drilling pipe portion whereby the inner pipe portion (21') of the safety release part has a mechanical buckling resistance that is lower than the buckling resistance of the inner pipe (21).
5. Drilling and anchoring device according to claim 4, characterized in that the mechanical safety device release part (22) is located close to an injection head (23) of the device,
6. Drilling and anchoring device according to any claims 3 to 5, characterized in that the drilling tool (12) is coupled in an axially separable manner to the injection tool, said injection tool comprising cement injection nozzles (13, 14, 16)
7. Drilling and anchoring device according to claim 6, characterized in that there are at least two of said cement injection nozzles which are arranged in the injection tool in radially opposite manner.
8. Drilling and anchoring device according to claim 7, characterized in that said injection nozzles which are arranged in a radially opposite manner are so oriented that the cement is injected in a direction essentially orthogonal to the central axis of the drilling pipe.
9. Drilling device according to claim 6, characterized in that at least one of the injection nozzles (16) is oriented toward the drilling tool in order to facilitate the separation of the injection tool from the drilling tool during cement injection.

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